2. Classification of some organic compounds
- Aliphatic compounds
The aliphatic hydrocarbons are subdivided into three groups
of homologous series according to their state of saturation:
•paraffins, which are alkanes without any double or triple
•olefins or alkenes which contain one or more double
bonds, i.e. di-olefins (dienes) or poly-olefins.
•alkynes, which have one or more triple bonds.
5. Organic Compounds Structural Theory. Butlerov. 1861.
1. An atom of an element in organic compound can form a
fixed number of bonds. Carbon is tetravalent.
2. A carbon atom use one or more of it's valences to form
bonds to other carbons. Thus, there are isomers. Isomers
are different compounds that have the same molecular
formula but differ in the order in which their atoms are
3. Atoms are influence upon each other.
6. 1. Types of Hybridisations.
Hybridisation describes the bonding atoms from an atom's
point of view. That is, for a tetrahedrally coordinated carbon
(e.g., methane, CH4), the carbon should have 4 orbitals with
the correct symmetry to bond to the 4 hydrogen atoms. The
problem with the existence of methane is now this: carbon's
ground-state configuration is 1s2 2s2 2px
1 or more easily
7. Therefore, the 2s orbital (core orbitals are almost never
involved in bonding) "mixes" with the three 2p orbitals to
form four sp3 hybrids (read as s-p-three). See graphical
8. Carbon forms 4 bonds:
347 kJ/mol for C—C bonds, 0.154 nm,
Tetrahedral, angle 109.5º
9. In sp2 hybridisation the 2s orbital is mixed with only
two of the three available 2p orbitals:
forming a total of 3 sp2 orbitals with one p-orbital remaining. In
ethylene (ethene) the two carbon atoms form a σ bond by overlapping
two sp2 orbitals and each carbon atom forms two covalent bonds with
hydrogen by s–sp2 overlap all with 120° angles. Ethylene (ethene),
showing the pi bond in green.
Like single covalent bonds, double bonds can
be described in terms of overlapping atomic
orbitals, except that, unlike a single bond
(which consists of a single sigma bond), a
carbon-carbon double bond consists of one
sigma bond and one pi bond. This double
bond is stronger than a single covalent bond
(611 kJ/mol for C=C vs. 347 kJ/mol for C—C)
and also shorter with an average bond
length of 0.133 nm, Planar, angle 120º.
11. The chemical bonding in compounds such as alkynes with triple bonds
is explained by sp hybridization.
In this model, the 2s orbital mixes with only one of the three
p-orbitals resulting in two sp orbitals and two remaining
unchanged p orbitals. The chemical bonding in acetylene
(ethyne) (C2H2) consists of sp–sp overlap between the two
carbon atoms forming a σ bond and two additional π bonds
formed by p–p overlap. Each carbon also bonds to hydrogen
in a sigma s–sp overlap at 180° angles, 839 kj/mol, linear,
13. • There appears to be almost no limit to the number of
different structures that carbon can form.
• Neighboring carbon atoms can form double and triple
bonds in addition to single carbon-carbon bonds.
• Single bond: Double bond: Triple bond:
• Isomerism refers to the occurrence of two or
more compounds having the same molecular
• Therefore, isomers are defined as molecules
that have the same molecular formula but
have a different arrangement of the atoms.
• There are 2 main types of isomerism:
- structural isomerism
geometrical isomerism optical isomerism
• Structural isomerism occurs in compounds
having the same molecular formula but
different structural formula.
• They differ from the way the atoms are
bonded to one another.
• Structural isomers have different physical
properties such as melting point, boiling
point and density.
• They might have different chemical
properties if the isomers are from different
• For example, propanoic acid (C3H6O2) reacts
with aqueous sodium carbonate to liberate
carbon dioxide, but ethyl methanoate
(C3H6O2) does not.
• Geometrical isomerism (or sometimes known
as cis- trans isomerism) occurs in compounds
having the carbon-carbon double bond, C=C,
or cyclic compounds, which hinders free
rotation of the groups in the molecule.
• Geometrical isomers usually have similar chemical
properties because they are from the same
• Geometrical isomers differ in their physical
Structural isomers of butene
Property Cis-but-2-ene Trans-but-2-ene
Melting point / K 134.2 167.6
Boiling point / K 278.0 274.0
Density / gdm-3 0.621 0.604
23. Hydrocarbons Reactivity
•Homolysis of the bond.
Cl··Cl → 2Cl· Radical (R)
•Heterolysis of the bond.
Cl:Cl → Cl + + :Cl-
Electrophile ( E)-positive (Cl+)
Nucleophile (N)-negative (Cl-)
26. Substitution Mechanism (SR) or
Free Radical Halogenation.
In organic chemistry, free radical halogenation is a
type of halogenation. This chemical reaction is
typical for alkanes and alkyl-substituted aromatics
under application of heat or UV light. The reaction
is used for the industrial synthesis of chloroform
(CHCl3), dichloromethane (CH2Cl2), and
hexachlorobutadiene. It proceeds by a free radical
29. In the case of methane or ethane, all the hydrogen atoms
are equivalent and have an equal chance of being replaced.
This leads to what is known as a statistical product
distribution. For propane and higher alkanes, the hydrogen
atoms which form part of CH2 (or CH) groups are
The reaction of alkanes with fluorine is difficult to control,
that with chlorine is moderate to fast, that with bromine is
slow and requires high levels of UV irradiation while the
reaction with iodine is practically non-existent.
30. •primary carbon atom: one carbon neighbor
•secondary carbon atom: two carbon neighbors
•tertiary carbon atom: three carbon neighbors
•quaternary carbon atom: four carbon neighbors
31. Radical stability: tertiary radical species are more
stable than secondary radical species, and
secondary radical species are more stable than
primary radical species--thus any single
chlorination will favor substitution at the most
33. The principal carbon-containing products of
incomplete ethane combustion are single-carbon
compounds such as carbon monoxide and
formaldehyde. One important route by which the
carbon-carbon bond in ethane is broken to yield
these single-carbon products is the decomposition
of the ethoxy radical into a methyl radical and
formaldehyde, which can in turn undergo further
Oxidation [O] :
CH3-CH3 → CH3CH2OH → CH3COH → CH3COOH
40. The rule may be summarized as "the rich get
richer": a carbon rich in substituents will gain
more substituents and the carbon with more
hydrogens attached will get the hydrogen in
many organic addition reactions.
Order of stability of examples of tertiary (III),
secondary (II), and primary (I) alkyl carbocations.
47. Electronic effects.
1. The inductive effect (I) in Chemistry and Physics is an
experimentally observable effect of the transmission of
charge through a chain of atoms in a molecule by
electrostatic induction.The net polar effect exerted by a
substituent is a combination of this inductive effect and the
The electron cloud in a σ-bond between two unlike atoms is
not uniform and is slightly displaced towards the more
electronegative of the two atoms. This causes a permanent
state of bond polarization, where the more electronegative
atom has a slight negative charge(δ-) and the other atom
has a slight positive charge(δ+).
48. The inductive effect may be caused by some molecules also.
Relative inductive effects have been experimentally
measured with reference to hydrogen.
49. 2. The mesomeric effect (M) or resonance effect in
chemistry is a property of substituents or functional groups
in a chemical compound. The effect is used in a qualitative
way and describes the electro withdrawing or releasing
properties of substituents based on relevant resonance
structures and is symbolized by the letter M. The mesomeric
effect is negative (-M) when the substituent is an electron-
withdrawing group and the effect is positive (+M) when
based on resonance the substituent is an electron releasing
50. In chemistry, a conjugated system is a system of
connected p-orbitals with delocalized electrons in
compounds with alternating single and multiple bonds,
which in general may lower the overall energy of the
molecule and increase stability. Lone pairs, radicals may be
part of the system. The compound may be cyclic, acyclic,
linear or mixed.
A conjugated system has a region of overlapping p-orbitals,
bridging the interjacent single bonds. They allow a
delocalization of pi electrons across all the adjacent aligned
p-orbitals. The pi electrons do not belong to a single bond or
atom, but rather to a group of atoms.
51. Conjugated systems form the basis of
chromophores, which are light-absorbing parts
of a molecule that can cause a compound to be
1,3-Butadiene is a simple conjugated diene with the
The name butadiene can also refer to the isomer,
1,2-butadiene, which is a cumulated diene
55. Mesomeric effect can be transmitted along any
number of carbon atoms in a conjugated
system. This accounts for the resonance
stabilization of the molecule due to
delocalization of charge.
56. In eastern Europe, China, and India, butadiene is also
produced from ethanol. While not competitive with steam
cracking for producing large volumes of butadiene, lower
capital costs make production from ethanol a viable option
for smaller-capacity plants. Two processes are in use.
In the single-step process developed by Sergei Lebedev,
ethanol is converted to butadiene, hydrogen, and water at
400–450 °C over any of a variety of metal oxide catalysts:
2 CH3CH2OH → CH2=CH-CH=CH2 + 2 H2O + H2
57. This process was the basis for the Soviet Union's
synthetic rubber industry during and after World War
II, and it remains in limited use in Russia and other
parts of eastern Europe.
58. In the other, two-step process, developed by the Russian
chemist Ivan Ostromislensky, ethanol is oxidized to
acetaldehyde, which reacts with additional ethanol over a
tantalum-promoted porous silica catalyst at 325–350 °C to
CH3CH2OH + CH3CHO → CH2=CH-CH=CH2 + 2 H2O
61. Alkyne CnH2n-2
Addition of hydrogen, halogens, and related
Alkynes characteristically undergo reactions that
show that they are "doubly unsaturated," meaning
that each alkyne unit is capable of adding two
equivalents of H2, halogens or related HX reagents
(X = halide, pseudohalide, etc.).
68. In organic chemistry, the structures of some rings of atoms are
unexpectedly stable. Aromaticity is a chemical property in which a
conjugated ring of unsaturated bonds, lone pairs, or empty orbitals
exhibit a stabilization stronger than would be expected by the
stabilization of conjugation alone. It can also be considered a
manifestation of cyclic delocalization and of resonance.
69. Aromaticity (aromatic rules)
An aromatic (or aryl) compound contains a set of
covalently-bound atoms with specific
•Coplanar structure, with all the contributing atoms in the
•A delocalized conjugated π system, most commonly an
arrangement of alternating single and double bonds
70. •Contributing atoms arranged in one or more rings
•A number of π delocalized electrons that is even, but not a
multiple of 4. That is, 4n + 2 number of π electrons, where
n=0, 1, 2, 3, and so on. This is known as Hückel's Rule.
71. Aromatic molecules typically display enhanced
chemical stability, compared to similar non-
aromatic molecules. This extra stability
changes the chemistry of the molecule.
Aromatic compounds undergo electrophilic
aromatic substitution, but not electrophilic
addition reactions as happens with carbon-
carbon double bonds.